Valuing of the critical layer thickness from the deading time constant of RHEED oscillation in the case of In x Ga 1x As=GaAs heterojunction A ´ kos Nemcsics * Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences, PO Box 49, H-1525 Budapest, Hungary Abstract In this work, we have looked for the correlation between the observed decay of reflection high-energy electron diffraction intensity oscillation and the critical layer thickness in the case of strained In x Ga 1x As=GaAs heterojunctions. The value of deading time constant of oscillation depends on the mismatch and on growth parameters, too. The decay of oscillation was described by two deading time constants which are responsible for the influences of the parameters mentioned above. The critical layer thickness was valued from the deading time constant responsible for the influence of mismatch only. The critical layer thickness determined this way shows good agreement with the theoretical model. # 2002 Elsevier Science B.V. All rights reserved. Keywords: III–V materials; MBE; RHEED; Heterojunction; Critical layer thickness 1. Introduction and preliminaries In x Ga 1x As=GaAs heteroepitaxy has a great impor- tance not only in the fabrication of semiconductor devices but this as a good model structure for the investigation of the strained layer growth. The critical layer thickness (CLT) in the heteroepitaxy was inves- tigated experimentally as well as theoretically [1]. Under real growth circumstances the measured CLT depends not only on misfit but on the growth para- meters, too [2]. The best in-situ way to monitor molecular-beam-epitaxy (MBE) deposition is reflec- tion high-energy electron diffraction (RHEED). RHEED intensity oscillations are used for accurate determination of the threshold layer thickness in two-dimensional growth mode which is technology dependent, too. The lattice mismatch also affects the behaviour of RHEED oscillations. The oscillation amplitude decreases rapidly during the In x Ga 1x As growth due to its strong dependence on the InAs mole fraction. This decrease also indicates the formation of the three-dimensional growth mode. The growth of In x Ga 1x As layers on GaAs (0 0 1) substrate was carried out by MBE at 490 8C deposition temperature. In this case, the accurate intensity of RHEED oscillations was measured directly by means of high resolution Faraday cup. The growth rate and the composition were determined by the help of RHEED oscillation while the composition ranged between x ¼ 0 and 0.4. The composition change was caused by the increase of In flux, while the other technological parameters remained unchanged. More details about this growth technology are described in [3]. The magnitude of intensity oscillations continu- ously decreases during the growth process. With the Applied Surface Science 190 (2002) 294–297 * Tel.: þ36-1-392-2222x3178; fax: þ36-1-392-2235. E-mail address: nemcsics@mfa.kfki.hu (A ´ . Nemcsics). 0169-4332/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0169-4332(01)00871-6